Web应用防护系统（也称：网站应用级入侵防御系统。英文：Web Application Firewall，简称： WAF）。利用国际上公认的一种说法：Web应用防火墙是通过执行一系列针对HTTP/HTTPS的安全策略来专门为Web应用提供保护的一款产品。本文介绍了常见的WAF指纹识别的一些技术，详见如下：
WAF指纹
Cookie值
Citrix Netscaler
“Citrix Netscaler”会在HTTP返回头部Cookie位置加入“ns_af”的值，可以以此判断为Citrix Netscaler的WAF，国内此类WAF很少（这货居然是searchsecurity认定的2013最好的防火墙）。
一个恶意的请求示例：
GET / HTTP/1.1
Host: target.com
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:25.0) Gecko/20100101 Firefox/25.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Cookie: ASPSESSIONIDAQQSDCSC=HGJHINLDNMNFHABGPPBNGFKC; ns_af=31+LrS3EeEOBbxBV7AWDFIEhrn8A000;ns_af_.target.br_%2F_wat=QVNQU0VTU0lPTklEQVFRU0RDU0Nf?6IgJizHRbTRNuNoOpbBOiKRET2gA&
Connection: keep-alive
Cache-Control: max-age=0
F5 BIG IP ASM
F5 BiG IP ASM会在Cookie中加入“TS+随机字符串”的Cookie信息，一个非恶意的请求如下：
GET / HTTP/1.1
Host: www.target.com
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:25.0) Gecko/20100101 Firefox/25.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Cookie: target_cem_tl=40FC2190D3B2D4E60AB22C0F9EF155D5; s_fid=77F8544DA30373AC-31AE8C79E13D7394; s_vnum=1388516400627%26vn%3D1; s_nr=1385938565978-New; s_nr2=1385938565979-New; s_lv=1385938565980; s_vi=[CS]v1|294DCEC0051D2761-40000143E003E9DC[CE]; fe_typo_user=7a64cc46ca253f9889675f9b9b79eb66; TSe3b54b=36f2896d9de8a61cf27aea24f35f8ee1abd1a43de557a25c529fe828; TS65374d=041365b3e678cba0e338668580430c26abd1a43de557a25c529fe8285a5ab5a8e5d0f299
Connection: keep-alive
Cache-Control: max-age=0
HTTP响应
Mod_Security
Mod_Security是为Apache设计的开源Web防护模块，一个恶意的请求Mod_Security会在响应头返回“406 Not acceptable”的信息。
请求：
GET /<script>alert(1);</script>HTTP/1.1 Host: www.target.com User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:25.0) Gecko/20100101 Firefox/25.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate Connection: keep-alive 响应： HTTP/1.1 406 Not Acceptable Date: Thu, 05 Dec 2013 03:33:03 GMT Server: Apache Content-Length: 226 Keep-Alive: timeout=10, max=30 Connection: Keep-Alive Content-Type: text/html; charset=iso-8859-1 <head><title>Not Acceptable!</title></head><body><h1>Not Acceptable!</h1><p>An appropriate representation of the requested resource could not be found on this server. This error was generated by Mod_Security.</p></body></html>
WebKnight
WebKnight是用来设计在IIS下面使用的WAF设备，较为常见。WebKnight会对恶意的请求返回“999 No Hacking”的信息。
请求：
GET /?PageID=99<script>alert(1);</script>HTTP/1.1 Host: www.aqtronix.com User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:25.0) Gecko/20100101 Firefox/25.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate Connection: keep-alive 响应： HTTP/1.1 999 No Hacking Server: WWW Server/1.1 Date: Thu, 05 Dec 2013 03:14:23 GMT Content-Type: text/html; charset=windows-1252 Content-Length: 1160 Pragma: no-cache Cache-control: no-cache Expires: Thu, 05 Dec 2013 03:14:23 GMT
F5 BIG IP
F5 BIG IP会对恶意请求返回“419 Unknown”的信息，如下：
GET /<script> HTTP/1.0 HTTP/1.1 419 Unknown Cache-Control: no-cache Content-Type: text/html; charset=iso-8859-15 Pragma: no-cache Content-Length: 8140 Date: Mon, 25 Nov 2013 15:22:44 GMT Connection: keep-alive Vary: Accept-Encoding
dotDefender
dotDefender用来防护.net的程序，也比较出名，会对恶意请求返回“dotDefender Blocked Your Request”的信息。
请求：
GET /---HTTP/1.1
Host: www.acc.com
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:25.0) Gecko/20100101 Firefox/25.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
Cache-Control: max-age=0
响应：
HTTP/1.1 200 OK Cache-Control: no-cache Content-Type: text/html Vary: Accept-Encoding Server: Microsoft-IIS/7.5 X-Powered-By: ASP.NET Date: Thu, 05 Dec 2013 03:40:14 GMT Content-Length: 2616 <!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd"><htmlxmlns="http://www.w3.org/1999/xhtml"><head><title>dotDefender Blocked Your Request</title>
……
特定资源文件
部分特定WAF在返回的告警页面含特定的CSS或者JS文件，可以作为判断的依据，这类情况在WAF类里比较少，实际也可以归并到HTTP响应中。
看2个样例：
<html><bodystyle="margin:0; padding:0"><center><iframewidth="100%"align="center"height="870"frameborder="0"scrolling="no"src="http://safe.webscan.360.cn/stopattack.html"></iframe></center></body></html> HTTP/1.1 405 Not Allowed Server: ASERVER/1.2.9-3 Date: Fri, 27 Dec 2013 14:15:14 GMT Content-Type: text/html Connection: keep-alive X-Powered-By-Anquanbao: MISS from uni-tj-ky-sb3 Content-Length: 7188 <divclass="wrapper"><divclass="titlelogo"></div><divclass="err_tips">由于您访问的URL有可能对网站造成安全威胁，您的访问被阻断。</div><divclass="feedback"><formaction="http://report.anquanbao.com/api.php"method="post"><inputtype="hidden"name="black_code"value=""class="hidden_rule_id"/><inputtype="hidden"name="deny_time"value=""class="hidden_intercept_time"/><inputtype="hidden"name="server_id"value=""class="hidden_server_title"/><inputtype="hidden"name="deny_url"value=""class="deny_url"/><inputtype="submit"class="submit_img"value=""/></form></div><divclass="detailcontent"><divclass="detailupimg"><ahref="javascript:;">站长点击查看详情</a></div><divclass="detaildownimg "><ahref="javascript:;">站长点击查看详情</a></div><divclass="hiddeninfo"> 规则ID:<spanclass="rule_id">10384</span><spanstyle="margin-left:20px">拦截时间：</span><spanclass="intercept_time">2013/12/27 22:15:14</span><divclass="hiddeninfosecond"><spanstyle="padding-top:20px">ServerName：</span><spanclass="server_title"style="padding-top:20px">uni-tj-ky-sb3/1.2.9-3</span></div><divclass="hiddeninfothird">
WAF识别工具
一些WAF可以自定义返回的消息内容，或者全部返回自定义的404页面或200页面，有一些工具会协助作为WAF设备的识别。
Wafw00f
用python编写的一个小工具，开源地址：
http://code.google.com/p/waffit/source/browse/trunk/wafw00f.py
Wafw00f用来判断WAF设备的函数如下：
AdminFolder = '/Admin_Files/' xssstring = '<script>alert(1)</script>' dirtravstring = '../../../../etc/passwd' cleanhtmlstring = '<invalid>hello' isaservermatch = 'Forbidden ( The server denied the specified Uniform Resource Locator (URL). Contact the server administrator. )'
使用“python wafw00f.py -h”可以查看工具的使用方法，运行示例：
python wafw00f.py http://www.victim.org/
基于Cookie的检测
Wafw00f的探测大部分是基于Cookie的检测。
F5asm的检测规则如下：
def isf5asm(self):
# credit goes to W3AF
return self.matchcookie('^TS[a-zA-Z0-9]{3,6}=')
基于响应头的检测
Profense在响应头会包含'server','profense'的信息。
def isprofense(self):
"""
Checks for server headers containing "profense"
"""
return self.matchheader(('server','profense'))
sqlmap
Sqlmap是一款检测和利用SQLi漏洞工具，也是基于python编写，业内认同率较高，sqlmap用来探测WAF类型想比较Wafw00f来说还多一些。
参考：
https://github.com/sqlmapproject/sqlmap/tree/master/waf
Sqlmap用来探测每种WAF设备都是一个python文件，同样是从cookie信息或者返回头信息进行判断。
以Mod_Security为例
#!/usr/bin/env python
"""
Copyright (c) 2006-2013 sqlmap developers (http://sqlmap.org/)
See the file 'doc/COPYING' for copying permission
"""
import re
from lib.core.enums import HTTP_HEADER
from lib.core.settings import WAF_ATTACK_VECTORS
__product__ = "ModSecurity: Open Source Web Application Firewall (Trustwave)"
def detect(get_page):
retval = False
for vector in WAF_ATTACK_VECTORS:
page, headers, code = get_page(get=vector)
retval = code == 501 and re.search(r"Reference #[0-9A-Fa-f.]+", page, re.I) is None
retval |= re.search(r"Mod_Security|NOYB", headers.get(HTTP_HEADER.SERVER, ""), re.I) is not None
if retval:
break
return retval
Sqlmap用来探测WAF的命令如下：
python sqlmap.py -u “http://www.victim.org/ex.php?id=1” --identify-waf
貌似必须是或自己修改的类似动态参数才能使用。
xenoitx
检测和利用XSS漏洞的神器，WAF检测也是其中的功能之一。